Intercepting memory operations of a guest

Sorry for any cross posting. I sent this to some of the other lists as well.

I'm wanting to modify some xen source code for the purposes of some research, exploration, and testing of some security concepts.

I have a few questions after looking through the source.

All of the below applies to 32-bit guests.

#1: Is there anyway possible to trap/insert some code at/hook into, any modification of a PV guest's page table. Anything like a hypercall handler I can plugin to, a function or series of functions that always gets called, something I can provide a call back to, or anything else?

#2: For some research purposes, I plan on replicating portions of the page table of a guest, only those pages of the guest's kernel. I hope to do this by the supervisory bit being set; however, I welcome any suggestions of a better approach to detecting when kernel pages are being modified?

In general, to explain any questions I haven't specifically asked above; I'm looking for the appropriate place in xen to intercept any writes, reads, and executes of a guest's memory.

Also, would such activities be easier or more difficult with hvm guests? Since xen has to provide hvm guests an individual CR3, would such a place be much easier to hook into because of any abstraction layers that already exist for such things?

The only reason I picked pv guests was that the semantics of what is a kernel page and what is not might not be as easy to determine in an hvm guest, but perhaps this is not the case?